1. Field of the Invention
This invention relates to a turbocharger.
2. Related Art
Turbochargers have been extensively used in automobiles since they can further enhance the performance of an engine. The turbocharger includes a housing, and a turbine shaft supported in a center hole in the housing through bearings. In such a conventional turbocharger, the bearings are supplied with engine oil to be lubricated. Therefore, many holes serving as passages for engine oil are formed in the small housing of the turbocharger as described in JP-A-5-141259 and JP-A-10-19045.
In the turbochargers described in JP-A-5-141259 and JP-A-10-19045, many holes are formed in a body portion of the housing as described above. Therefore, from the viewpoint of a space, it is difficult to form a coolant passage (for cooling the turbocharger) in the body portion of the small housing, and besides a cooling water jacket can be formed only at part of the body portion. Therefore, there is encountered a problem that a cooling effect by a coolant is low, and therefore the temperature of the bearing becomes high, so that seizure is liable to occur. Furthermore, the amount of oil to be supplied to the bearing is determined by the size (or diameter) of the holes formed in the housing, and therefore there is encountered a problem that the amount of oil to be supplied to the bearing can not be adjusted with the use of these holes.
Furthermore, in the turbochargers described in JP-A-5-141259 and JP-A-10-19045, engine oil contaminated with foreign matters such as carbon sludge produced at the engine is supplied to the bearing. Therefore, particularly when the bearing is a rolling bearing, it is feared that seizure may develop in this rolling bearing when such foreign matters is introduced into the rolling bearing. Therefore, a filter or the like for removing such foreign matters is provided in an intermediate portion of the engine oil passage. Even in this case, the foreign matters can not be completely removed.